# Electricity?

I don’t get the difference between a variable resistor and a potentiometre, don’t both just vary the voltage across a component?

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Essentially, a potentiometer is a three terminal device, the two ends of a resistor and a wiper. Typically a full signal voltage is applied across the whole resistor and the wiper taps off a proportion of the signal, ie it is considered as a potential divider.

Whereas a variable resistor is two terminals, one end of the resistor and the wiper, ie functioning as just a variable resistor.

Of course you can use a device fabricated as a potentiometer as a variable resistor, and equally, most variable resistors have both ends available for connection...

Generally, devices made for frequent adjustment such as a volume knob, are built as potentiometers and the physical units are referred to as potentiometers regardless of how they are wired up, but electrically in describing a circuit's operation, we would call it a variable resistor if that was its function.

Many variable resistors are only ever adjusted at manufacture or in maintenance and they look nothing like pots, they are generally mounted direct to the pcb, often called a trimmer (eg cermet trimmer)..

• Dixon
Lv 7
8 months agoReport

No

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• Variable Resistor

Potentiometer

Rheostat

Similar

All are variable resistance components.

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• A variable resistor varies the resistance. A potentiometer (as it's name suggests) varies a potential; but confusingly, it does so using resistance. The potentiometer can be thought of as two resistors wired in series. This means that we can make three connections to it: one at each end and another at the middle where the two are joined. The wiper of the potentiomer effectiely divides the resistance of track into two. If the wiper is in the middle of the track and it is a linear potentiometer then it will divide the Track into two equal resistance parts meaning that the wiper will have half the voltage that appears between the two ends of the potentiometer.By varying the position of the wiper on the track we can vary the ratio of the two resistance parts of the track and so we can vary the voltage output from the wiper between the voltage values that appears at the two end points.

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• Potentiometer has three terminals whereas a variable resistor has only two terminals.

A potentiometer can be constructed as a variable resistor by using just two terminals (the centre pin and any other pin), but a variable resistor cannot be contructure as a potentiometer.Both parts have their own usage on circuit.

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• A variable resistor has a fixed voltage drop across is and changing the resistance changes the current. All the current goes through it.

A potentiometer lets you select a voltage somewhere between the maximum voltage and “ground” or whatever the minimum voltage is. The current can be split, because a potentiometer has 3 terminals.

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• They are similar. A variable resistor technically would have just two terminal, and the resistance between those terminals would be variable. A potentiometer is a 3 terminal device - both ends of the resistor are available as is an adjustable wiper. A pot can be used as a variable voltage divider.

A pot can be turned into an adjustable resistor by connecting the wiper to one end of the resistor, turning a 3 terminal device into a 2 terminal device.

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• "don’t both just vary the voltage across a component" NO, they do not. Neither one does that in itself.

They are both variable resistors, but the potentiometer is a three terminal device with a fixed resistor (say 100 Ω) and a sliding tap that gives you a variable resistance with the resistance from the tap to one end increasing (say 0 to 100 Ω) while the resistance from the tap to the other end decreasing (say 100 to 0 Ω).

The plain variable resistor, more correctly a rheostat, has two terminals and the resistance between them varies as the control is moved, say from 0 to 100 Ω for a 100 Ω rheostat.

They can both be setup to produce a variable voltage if a battery is used. In the case of the rheostat, a fixed resistor is needed also.

Note that the potentiometer can be used as a rheostat if you just use two of the three terminals.

Note also that rheostats are usually power devices, and potentiometers are not.

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